The Administrator has to activate this by clicking Settings → CRM → Fields → Order & opportunities: 
Users can then choose their own probability of an opportunity:
Articles in this section
- Change log: Tracking changes made to orders and opportunities
- Upselling in Subscriptions in Upsales
- Q: How do users choose the probability for an opportunity stage?
- Sales process BASIC
- How to use won/lost buttons with Opportunities
- Competitors overview
- Sales process guide: Reasons to verify your lead's budget
- How to define stakeholders & job titles in the Sales process
- Partner sales: How to add multiple companies to opportunities, subscriptions or orders
- How to upload documents and files